The effect of coincidental exposure of animals to oncogenic viruses and chemical carcinogens will be studied. N-nitroso compounds (known carcinogens) will be administered to animals in conjunction with two DNA-containing tumor viruses: simian virus-40 (SV40) or herpes simplex virus type 1 (HSV-1). In one approach virus-specific tumors will be induced with SV40 and the effect of carcinogens on these tumors will be studied. In a second approach, HSV-1, a virus with oncogenic potential but not usually causing experimental tumors in vivo will be given with suboptimal doses on N-nitroso compounds and possible synergism in the formation of tumors will be examined. Lastly, we will examine the role of virus infection on tumor induction by known chemical carcinogens. Evidence has already been obtained in this laboratory indicating that non-toxic doses of nitrosomethylurea can enhance herpesvirus specific transformation in vitro. It has been demonstrated that the maximum transformation rate occurs subsequent to the maximum alkylation of cell DNA. It is in light of this in vitro evidence, as well as work by others, that we have been encouraged to show in vivo cocarcinogenesis of chemical carcinogens with DNA tumor viruses.